The present invention relates to compositions containing a blend of chlorinated vinyl resins (such as polyvinyl chloride) and cellullosic materials (such as wood flour) which have excellent melt flow and melt strength for forming foamed and unfoamed extrudates having a high quality appearance. More specifically, the present invention relates to particular compositions of chlorinated vinyl resins, thermal stabilizers, lubricants, high molecular weight (“MW”) polymer processing aids, and a relatively high amount (greater than about 24 weight percent total) of cellulosic materials which form free flowing powders. Such compositions are readily extruded and can be formed into various foamed and unfoamed composite articles used in various applications, including building and construction products, such as fencing, siding, decking, window frames, sills, and doors. The present invention also relates to processes for preparing powder mixtures of such blend compositions which are readily extruded and thereby overcome the problems of pre-drying or pelletization as currently practiced. The present invention relates to a process for preparing free-flowing powders wherein up to 25 weight percent of the total added components can initially be water. The present invention also relates to a process for preparing foamed extrudates having an increased expansion ratio. Furthermore, the present invention relates to composites containing the compositions of the present invention.
Typically when high weight percentages of wood flour are blended with PVC, the resulting compound exhibits a high moisture content, poor powder handling properties (poor powder flow and low bulk density), poor melt flow and melt strength, and the finished part has a rough surface with edge tearing. Until now, previous attempts at combining wood flour and PVC have been limited to about a 20 percent weight percentage of the final composition as wood flour. Above 20 percent wood flour these problems are magnified and extrusion can not be readily performed.
Others have overcome these problems by pre-drying the wood flour (“WF”) before combining with PVC in preparing powder blends, predrying the powder blend before extrusion, or by first forming the PVC/WF powder blend into pellets. Such practices are both costly and time-consuming.
In U.S. Pat. No. 5,847,016, Cope describes a two step process for preparing PVC and wood flour composites wherein the wood flour particles are encapsulated by the PVC and pelletized. The pellets are subsequently mixed with additional PVC resin and blowing agent and extruded into a finished product. The encapsulation is believed to prevent moisture absorption in the pellets which affects the ability to extrude PVC/WF composites into foam. The total weight percent of wood flour in the disclosed PVC/WF compositions is limited to only about 17%.
In Japanese patent publication JP 95-315193, Murakami et al. describe foamable vinyl chloride resin I wood flour compositions in which the compositional components are formed into pellets and subsequently extruded or molded into parts. Murakami's compositions have total amounts of lubricants and processing aids which are fixed relative to that of the PVC amounts. As a result, the weight percentages of total lubricants and processing aids were decreased as the amount of wood flour was increased. As demonstrated herein, such compositions are not readily extrudable directly into smooth extrudates when in a powder form.
Similarly, it is known to simply add WF to a typical PVC formulation. This results in the total weight percentages of several key components (lubricants, high MW polymer processing aids and blowing agent) being considerably reduced as the amount of WF is increased. When this occurs, we have observed that process performance is greatly reduced.
We have heretofore discovered that in order to provide powder blends of a chlorinated vinyl resin (e.g., PVC) and a cellulosic material (e.g., WF) which are readily processable into foam extrudates having good appearance, it is important to maintain the weight percentages of the total lubricants and total high MW polymer processing aids based on the total blend composition at a level commensurate with that of a standard PVC foam formulation not containing WF. Therefore, as the amounts of cellulosic materials are increased, a concomitant increase in total lubricants and processing aids is required. The compositions and the process for preparing these powder compositions described herein contain a high weight percentage of cellulosic materials (hereinafter “CM”), greater than or equal to 24 percent by weight and at least one chlorinated vinyl resin (hereinafter “CVR”). These compositions not only are directly extrudable (and therefore do not require first pelletization of the composition or pre-drying of the cellulosic material component), but also provide extrudates having a good appearance. Until now, such compositions and processes have been heretofore unknown.
One object of the present invention is to provide extrudable chlorinated vinyl resin/cellulosic blend powder compositions that are readily extrudable into foamed and nonfoamed articles. A second object of the present invention is to provide extrudable polyvinyl chloride/wood flour blend powder compositions that are also free flowing powders which are readily extrudable into foamed and nonfoamed articles. A third object of the present invention is to provide a process for preparing the powder compositions according to the first object of the present invention. A fourth object of the present invention is to provide a process for preparing the powder blend composition according to the second object of the present invention wherein up to 25 weight percent of the total components added to the process can be water that is subsequently removed. A fifth object of the present invention is to provide a process for preparing a foamed extrudate having an increased expansion ratio. A sixth object of the present invention is to provide a composite having a substrate layer and at least one capstock layer made from the extrudable polyvinyl chloride/wood flour blend powder compositions according to the second object of the present invention. These and other objects as will become apparent from the following disclosure are achieved by the present invention.